The following snippets show how one can easily interact with the clipboard from QML code with the help of a tiny C++ wrapper / adapter. This code should work for all QML versions.

The C++ code is very simple and straight forward:

#ifndef QMLCLIPBOARDADAPTER_H
#define QMLCLIPBOARDADAPTER_H

#include <QApplication>
#include <QClipboard>
#include <QObject>

class QmlClipboardAdapter : public QObject
{
    Q_OBJECT
public:
    explicit QmlClipboardAdapter(QObject *parent = 0) : QObject(parent) {
        clipboard = QApplication::clipboard();
    }

    Q_INVOKABLE void setText(QString text){
        clipboard->setText(text, QClipboard::Clipboard);
        clipboard->setText(text, QClipboard::Selection);
    }

private:
    QClipboard *clipboard;
};

#endif // QMLCLIPBOARDADAPTER_H

Registration of our adapter is done as usual in the main.cpp file:

#include <QtDeclarative>
...
#include "qmlclipboardadapter.h"

Q_DECL_EXPORT int main(int argc, char *argv[])
{
    ...
    qmlRegisterType("meepasswords", 1, 0, "QClipboard");
    ...
}

And finally the clipboard can be used from QML code:

...
import meepasswords 1.0
...
    QClipboard{
        id: clipboard
    }
...
    onAccepted: clipboard.setText("foo")
...

Note that this implementation is a write-only clipboard. Though, modifying the above code to enable a read-write clipboard is straight forward.